CVE-2021-20218: Kubernetes client Improper Limitation Of A Pathname Vulnerability

HIGH
Advisory Identifier: GHSA-jwh2-ffg4-48xc
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CVSS 7.4
CWE-22
Published
Advisory Summary

CVE-2021-20218 is a HIGH (CVSS 7.4) improper limitation of a pathname vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting Kubernetes client libraries in the Maven ecosystem. The issue involves improper limitation of a pathname to a restricted directory in fabric8 kubernetes client. Remediation is available by upgrading affected packages to version 4.7.2, 4.11.2, 4.13.2, 5.0.2.

CVE-2021-20218 at a Glance

CVE Identifier CVE-2021-20218
GHSA Identifier GHSA-jwh2-ffg4-48xc
Severity HIGH
CVSS v3.1 Base Score 7.4
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product Kubernetes client
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 7.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-20218

To remediate this vulnerability, upgrade all affected Kubernetes client dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

io.fabric8:kubernetes-client fixed: 4.7.2 
<dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>4.7.2</version>
</dependency>
io.fabric8:kubernetes-client fixed: 4.11.2 
<dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>4.11.2</version>
</dependency>
io.fabric8:kubernetes-client fixed: 4.13.2 
<dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>4.13.2</version>
</dependency>
io.fabric8:kubernetes-client fixed: 5.0.2 
<dependency>
    <groupId>io.fabric8</groupId>
    <artifactId>kubernetes-client</artifactId>
    <version>5.0.2</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=io.fabric8

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-20218, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=io.fabric8

Analyze the terminal output to locate any version of Kubernetes client in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.7.2), your application is affected.

Note: The mvn dependency:tree -Dincludes=io.fabric8 command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. In Kubernetes client, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

A flaw was found in the fabric8 kubernetes-client in version 4.2.0 and after. This flaw allows a malicious pod/container to cause applications using the fabric8 kubernetes-client `copy` command to extract files outside the working path. The highest threat from this vulnerability is to integrity and system availability. This has been fixed in kubernetes-client-4.13.2 kubernetes-client-5.0.2 kubernetes-client-4.11.2 kubernetes-client-4.7.2

CVE-2021-20218 Affected Kubernetes client Versions

4 component(s)
Fixed Versions:
4.7.24.11.24.13.25.0.2
Product / Package Ecosystem Affected Versions Fixed Version
io.fabric8:kubernetes-client
maven/io.fabric8/kubernetes-client
Maven
≥ 4.2.0
< 4.7.2
4.7.2
io.fabric8:kubernetes-client
maven/io.fabric8/kubernetes-client
Maven
≥ 4.8.0
< 4.11.2
4.11.2
io.fabric8:kubernetes-client
maven/io.fabric8/kubernetes-client
Maven
≥ 4.12.0
< 4.13.2
4.13.2
io.fabric8:kubernetes-client
maven/io.fabric8/kubernetes-client
Maven
≥ 5.0.0
< 5.0.2
5.0.2

References

NVD — CVE-2021-20218 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-20218
Kubernetes client Source Repository REPOSITORY
https://github.com/fabric8io/kubernetes-client/issues/2715
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=1923405

Frequently Asked Questions

What is CVE-2021-20218?
CVE-2021-20218 is a security vulnerability in Kubernetes client involving Improper Limitation of a Pathname to a Restricted Directory in Fabric8 Kubernetes Client under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which Kubernetes client versions are affected?
Affected versions include releases prior to 4.7.2, 4.11.2, 4.13.2, 5.0.2 across affected packages: io.fabric8:kubernetes-client.
What version fixes CVE-2021-20218?
Upgrading to 4.7.2, 4.11.2, 4.13.2, 5.0.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is kubernetes-client affected?
Yes, io.fabric8:kubernetes-client is affected in releases prior to 4.7.2, 4.11.2, 4.13.2, 5.0.2. Upgrade your dependency to 4.7.2, 4.11.2, 4.13.2, 5.0.2 or later.
What is the CVSS score of CVE-2021-20218?
CVE-2021-20218 has a CVSS v3.1 base score of 7.4 (HIGH) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H.
What CWE is associated with CVE-2021-20218?
CVE-2021-20218 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check Maven dependencies for CVE-2021-20218?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=io.fabric8'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jwh2-ffg4-48xc",
  "modified" : "2022-06-22T18:50:29Z",
  "published" : "2022-05-24T17:44:37Z",
  "aliases" : [ "CVE-2021-20218" ],
  "summary" : "Improper Limitation of a Pathname to a Restricted Directory in Fabric8 Kubernetes Client",
  "details" : "A flaw was found in the fabric8 kubernetes-client in version 4.2.0 and after. This flaw allows a malicious pod/container to cause applications using the fabric8 kubernetes-client `copy` command to extract files outside the working path. The highest threat from this vulnerability is to integrity and system availability. This has been fixed in kubernetes-client-4.13.2 kubernetes-client-5.0.2 kubernetes-client-4.11.2 kubernetes-client-4.7.2",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.fabric8:kubernetes-client"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0"
      }, {
        "fixed" : "4.7.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.7.1"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.fabric8:kubernetes-client"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.8.0"
      }, {
        "fixed" : "4.11.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.11.1"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.fabric8:kubernetes-client"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.12.0"
      }, {
        "fixed" : "4.13.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.13.1"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.fabric8:kubernetes-client"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0"
      }, {
        "fixed" : "5.0.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.0.1"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-20218"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fabric8io/kubernetes-client/issues/2715"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=1923405"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-06-22T18:50:29Z",
    "nvd_published_at" : "2021-03-16T21:15:00Z"
  }
}